CODEWITHSUNDEEP
javahibernatejpaproxylazy-loading
Andrey Minogin
Andrey Minogin

Reputation: 4616

How to convert a Hibernate proxy to a real entity object

During a Hibernate Session, I am loading some objects and some of them are loaded as proxies due to lazy loading. It's all OK and I don't want to turn lazy loading off.

But later I need to send some of the objects (actually one object) to the GWT client via RPC. And it happens that this concrete object is a proxy. So I need to turn it into a real object. I can't find a method like "materialize" in Hibernate.

How can I turn some of the objects from proxies to reals knowing their class and ID?

At the moment the only solution I see is to evict that object from Hibernate's cache and reload it, but it is really bad for many reasons.

Upvotes: 195

Views: 128155

Answers (12)

tenpigs pinget
tenpigs pinget

Reputation: 121

15 years later, Hibernate (version 6.6.0) introduce @ConcreteProxy annotation so that the real class can be known by the proxy when you have a lazy relation to a super-class : https://in.relation.to/2024/05/10/concrete-proxy/ It should be used carefully because to get the real type Hibernate will add a JOIN to read discriminator value when related object is loaded...

Upvotes: 0

Matthias
Matthias

Reputation: 12259

For those who need a "pure" JPA solution: If you don't mind modifying your entity, you can add a simple method to it:

class MyEntity {
  //...
  public MyEntity unproxy() {
    return this;
  }
}

This works because once calling this method against the proxy, the proxy will call the "real" method on the entity (which returns the entity and not the proxy).

Be are of this side-effect, however: NHibernate warning Narrowing proxy to - this operation breaks ==

Upvotes: 0

Vlad Mihalcea
Vlad Mihalcea

Reputation: 153810

Since Hibernate ORM 5.2.10, you can do it likee this:

Object unproxiedEntity = Hibernate.unproxy(proxy);

Before Hibernate 5.2.10. the simplest way to do that was to use the unproxy method offered by Hibernate internal PersistenceContext implementation:

Object unproxiedEntity = ((SessionImplementor) session)
                         .getPersistenceContext()
                         .unproxy(proxy);

Upvotes: 93

O.Badr
O.Badr

Reputation: 3131

Starting from Hiebrnate 5.2.10 you can use Hibernate.proxy method to convert a proxy to your real entity:

MyEntity myEntity = (MyEntity) Hibernate.unproxy( proxyMyEntity );

Upvotes: 6

Sergey Bondarev
Sergey Bondarev

Reputation: 420

I've written following code which cleans object from proxies (if they are not already initialized)

public class PersistenceUtils {

    private static void cleanFromProxies(Object value, List<Object> handledObjects) {
        if ((value != null) && (!isProxy(value)) && !containsTotallyEqual(handledObjects, value)) {
            handledObjects.add(value);
            if (value instanceof Iterable) {
                for (Object item : (Iterable<?>) value) {
                    cleanFromProxies(item, handledObjects);
                }
            } else if (value.getClass().isArray()) {
                for (Object item : (Object[]) value) {
                    cleanFromProxies(item, handledObjects);
                }
            }
            BeanInfo beanInfo = null;
            try {
                beanInfo = Introspector.getBeanInfo(value.getClass());
            } catch (IntrospectionException e) {
                // LOGGER.warn(e.getMessage(), e);
            }
            if (beanInfo != null) {
                for (PropertyDescriptor property : beanInfo.getPropertyDescriptors()) {
                    try {
                        if ((property.getWriteMethod() != null) && (property.getReadMethod() != null)) {
                            Object fieldValue = property.getReadMethod().invoke(value);
                            if (isProxy(fieldValue)) {
                                fieldValue = unproxyObject(fieldValue);
                                property.getWriteMethod().invoke(value, fieldValue);
                            }
                            cleanFromProxies(fieldValue, handledObjects);
                        }
                    } catch (Exception e) {
                        // LOGGER.warn(e.getMessage(), e);
                    }
                }
            }
        }
    }

    public static <T> T cleanFromProxies(T value) {
        T result = unproxyObject(value);
        cleanFromProxies(result, new ArrayList<Object>());
        return result;
    }

    private static boolean containsTotallyEqual(Collection<?> collection, Object value) {
        if (CollectionUtils.isEmpty(collection)) {
            return false;
        }
        for (Object object : collection) {
            if (object == value) {
                return true;
            }
        }
        return false;
    }

    public static boolean isProxy(Object value) {
        if (value == null) {
            return false;
        }
        if ((value instanceof HibernateProxy) || (value instanceof PersistentCollection)) {
            return true;
        }
        return false;
    }

    private static Object unproxyHibernateProxy(HibernateProxy hibernateProxy) {
        Object result = hibernateProxy.writeReplace();
        if (!(result instanceof SerializableProxy)) {
            return result;
        }
        return null;
    }

    @SuppressWarnings("unchecked")
    private static <T> T unproxyObject(T object) {
        if (isProxy(object)) {
            if (object instanceof PersistentCollection) {
                PersistentCollection persistentCollection = (PersistentCollection) object;
                return (T) unproxyPersistentCollection(persistentCollection);
            } else if (object instanceof HibernateProxy) {
                HibernateProxy hibernateProxy = (HibernateProxy) object;
                return (T) unproxyHibernateProxy(hibernateProxy);
            } else {
                return null;
            }
        }
        return object;
    }

    private static Object unproxyPersistentCollection(PersistentCollection persistentCollection) {
        if (persistentCollection instanceof PersistentSet) {
            return unproxyPersistentSet((Map<?, ?>) persistentCollection.getStoredSnapshot());
        }
        return persistentCollection.getStoredSnapshot();
    }

    private static <T> Set<T> unproxyPersistentSet(Map<T, ?> persistenceSet) {
        return new LinkedHashSet<T>(persistenceSet.keySet());
    }

}

I use this function over result of my RPC services (via aspects) and it cleans recursively all result objects from proxies (if they are not initialized).

Upvotes: 13

Ondro Mih&#225;lyi
Ondro Mih&#225;lyi

Reputation: 7710

I found a solution to deproxy a class using standard Java and JPA API. Tested with hibernate, but does not require hibernate as a dependency and should work with all JPA providers.

Onle one requirement - its necessary to modify parent class (Address) and add a simple helper method.

General idea: add helper method to parent class which returns itself. when method called on proxy, it will forward the call to real instance and return this real instance.

Implementation is a little bit more complex, as hibernate recognizes that proxied class returns itself and still returns proxy instead of real instance. Workaround is to wrap returned instance into a simple wrapper class, which has different class type than the real instance.

In code:

class Address {
   public AddressWrapper getWrappedSelf() {
       return new AddressWrapper(this);
   }
...
}

class AddressWrapper {
    private Address wrappedAddress;
...
}

To cast Address proxy to real subclass, use following:

Address address = dao.getSomeAddress(...);
Address deproxiedAddress = address.getWrappedSelf().getWrappedAddress();
if (deproxiedAddress instanceof WorkAddress) {
WorkAddress workAddress = (WorkAddress)deproxiedAddress;
}

Upvotes: 1

Sharky
Sharky

Reputation: 559

With Spring Data JPA and Hibernate, I was using subinterfaces of JpaRepository to look up objects belonging to a type hierarchy that was mapped using the "join" strategy. Unfortunately, the queries were returning proxies of the base type instead of instances of the expected concrete types. This prevented me from casting the results to the correct types. Like you, I came here looking for an effective way to get my entites unproxied.

Vlad has the right idea for unproxying these results; Yannis provides a little more detail. Adding to their answers, here's the rest of what you might be looking for:

The following code provides an easy way to unproxy your proxied entities:

import org.hibernate.engine.spi.PersistenceContext;
import org.hibernate.engine.spi.SessionImplementor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.jpa.repository.JpaContext;
import org.springframework.stereotype.Component;

@Component
public final class JpaHibernateUtil {

    private static JpaContext jpaContext;

    @Autowired
    JpaHibernateUtil(JpaContext jpaContext) {
        JpaHibernateUtil.jpaContext = jpaContext;
    }

    public static <Type> Type unproxy(Type proxied, Class<Type> type) {
        PersistenceContext persistenceContext =
            jpaContext
            .getEntityManagerByManagedType(type)
            .unwrap(SessionImplementor.class)
            .getPersistenceContext();
        Type unproxied = (Type) persistenceContext.unproxyAndReassociate(proxied);
        return unproxied;
    }

}

You can pass either unproxied entites or proxied entities to the unproxy method. If they are already unproxied, they'll simply be returned. Otherwise, they'll get unproxied and returned.

Hope this helps!

Upvotes: 2

Dmitry
Dmitry

Reputation: 3038

Thank you for the suggested solutions! Unfortunately, none of them worked for my case: receiving a list of CLOB objects from Oracle database through JPA - Hibernate, using a native query.

All of the proposed approaches gave me either a ClassCastException or just returned java Proxy object (which deeply inside contained the desired Clob).

So my solution is the following (based on several above approaches):

Query sqlQuery = manager.createNativeQuery(queryStr);
List resultList = sqlQuery.getResultList();
for ( Object resultProxy : resultList ) {
    String unproxiedClob = unproxyClob(resultProxy);
    if ( unproxiedClob != null ) {
       resultCollection.add(unproxiedClob);
    }
}

private String unproxyClob(Object proxy) {
    try {
        BeanInfo beanInfo = Introspector.getBeanInfo(proxy.getClass());
        for (PropertyDescriptor property : beanInfo.getPropertyDescriptors()) {
            Method readMethod = property.getReadMethod();
            if ( readMethod.getName().contains("getWrappedClob") ) {
                Object result = readMethod.invoke(proxy);
                return clobToString((Clob) result);
            }
        }
    }
    catch (InvocationTargetException | IntrospectionException | IllegalAccessException | SQLException | IOException e) {
        LOG.error("Unable to unproxy CLOB value.", e);
    }
    return null;
}

private String clobToString(Clob data) throws SQLException, IOException {
    StringBuilder sb = new StringBuilder();
    Reader reader = data.getCharacterStream();
    BufferedReader br = new BufferedReader(reader);

    String line;
    while( null != (line = br.readLine()) ) {
        sb.append(line);
    }
    br.close();

    return sb.toString();
}

Hope this will help somebody!

Upvotes: 1

0x6B6F77616C74
0x6B6F77616C74

Reputation: 2629

The another workaround is to call 

Hibernate.initialize(extractedObject.getSubojbectToUnproxy());

Just before closing the session.

Upvotes: 2

Yannis JULIENNE
Yannis JULIENNE

Reputation: 129

The way I recommend with JPA 2 :

Object unproxied  = entityManager.unwrap(SessionImplementor.class).getPersistenceContext().unproxy(proxy);

Upvotes: 10

Sanek Shu
Sanek Shu

Reputation: 237

Try to use Hibernate.getClass(obj)

Upvotes: 18

Bozho
Bozho

Reputation: 597114

Here's a method I'm using. 

public static <T> T initializeAndUnproxy(T entity) {
    if (entity == null) {
        throw new 
           NullPointerException("Entity passed for initialization is null");
    }

    Hibernate.initialize(entity);
    if (entity instanceof HibernateProxy) {
        entity = (T) ((HibernateProxy) entity).getHibernateLazyInitializer()
                .getImplementation();
    }
    return entity;
}

Upvotes: 261

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